Fast ionic conductors have considerable potential to enable technological development for energy storage and conversion. Hydride (H⁻) ions are a unique species because of their natural abundance, light mass, and large polarizability. Herein, we investigate characteristic H⁻ conduction, i.e., fast ionic conduction controlled by a pre-exponential factor. Oxygen-doped LaH₃ (LaH_3−2xO_x) has an optimum ionic conductivity of 2.6 × 10⁻² S cm⁻¹, which to the best of our knowledge is the highest H⁻ conductivity reported to date at intermediate temperatures. With increasing oxygen content, the relatively high activation energy remains unchanged, whereas the pre-exponential factor decreases dramatically. This extraordinarily large pre-exponential factor is explained by introducing temperature-dependent enthalpy, derived from H⁻ trapped by lanthanum ions bonded to oxygen ions. Consequently, light mass and large polarizability of H⁻, and the framework comprising densely packed H⁻ in LaH_3−2xO_x are crucial factors that impose significant temperature dependence on the potential energy and implement characteristic fast H⁻ conduction.

The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.